THE XAUTILUS. 53 



and angled above, rounded below, flattened on parietal margin. 

 Peristome continuous, not sinuous. 



Alt. 3 to 3-5 mm,, diam. 2 to 2-25 mm. 



Habitat, Lake Michigan, at Racine, Wis., in 30 fathoms. 



The shallow sutures and heavy texture are the more prominent 

 characters of this shell. In these points a resemblance to Hydrobia 

 ^dvce and other species of that group may be traced. From Amni- 

 cola lustrica the more flattened whorls at once separate this form. 



We are indebted to Dr. P. R. Hoy of Racine, Wis. for numerous 

 specimens. The species is named in honor of the late Professor 

 D. S. Sheldon of Davenport, Iowa, — one of the pioneer naturalists 

 of the Mississippi Valley. 



Amnicola lustrica Pilsbry. 



Shell slender, elevated, thin, translucent, wax-colored or slightly 

 brownish; whorls five, well rounded ; sutures deep; aperture ovate, 

 narrowed and slightly angled above ; jicristome entire, adherent to 

 body for a short distance above the narrow umbilicus. 



Alt. 4, diam. 2 to 2? mill. 



Habitat, New York to Illinois and Minnesota. 



A species of the Lake drainage. 



Say's Paludina lustrica has been referred by Haldeman and 

 Tryon to Pomatiopsis lapidaria. Binney also places it in Fomatlop- 

 sis, and the original of his fig. 189' is certainly an immature P. lap- 

 idaria, as I know by an examination Say's of original type. The 

 name lustrica has, however, been applied by some collectors to the 

 present species ; and while we must write lustrica Say a synonym 

 of P. lapidaria, the name may also stand in Amnicola for the well 

 known form described above. 



The species is variable in form as the figures'" show. It is nar- 

 rower than any other Amnicola, but wider than Bythinella Nicklini- 

 ana. In size and color, Bythinella obtusa is similar; but the acute 

 apex of lustrica will separate it from that blunt little species. 

 The animal and dentition are similar to A. limosa. 



1 Land and Fresh Water Shells, N. A. pt. II, 



- It is figured in a work now in preparation on the Mollusks of the Northern 

 U.S. 



